Process for the manufacture of ethylene



June117, 1941.

F. PORTER PROCESS FOR THE MANUFACTURE OF ETHYLENE Filed July 14, 1937 f Vez/,007.5 are Condensed condemsea 6'05 lNvraN-roRy 'WM Parier Patented June 17, 1941 E MANUFACTURE oF y rnocrss FoaE'rn THYLENE Frank Porter,v Syracuse, N. Solvay Process Company, corporation of New York Y., assignor to The New York, N. Y., a

Application July 14, 1937, 'Serial No. 153,495

7 Claims. (Cl. 260-683) v This invention relates to the manufacture of ethylene and is particularly directed to the cracking of mineral oils in order to obtain high yields of ethylene with a minimum formation of undesired icy-products.

It has in the past been proposed to manufacture ethylene by passing various hydrocarbon vapors or gases through a heated tube or other hot reaction zone in orde1` to effect the conversion of the hydrocarbon to ethylene.

lI have now found that hydrocarbons of the aliphatic series in general having a higher molecular weight than ethylene may be cracked to form high yields of ethylene provided'certain conditions are maintained during the cracking step. Thus, not only am I able to obtain a gas containing relatively high percentages of ethylene but also the liquid products from the reaction are reduced so that the quantities of hydrocarbons vwhich must be recycled or otherwise disposed o! are correspondingly diminished.

I have further found` that in the treatment of the higher mineral oils, for example the fractions of petroleum boiling above about 300 C., it is highly advantageous to subject the initial material to a preliminary combined low temperature cracking and hydrogenation before subjecting it to the high temperature vapor phase cracking process. .The low temperature combined hydrogenation and cracking appears to serve the purpose of converting the less volatile petroleum constituents to reaction products which may be cracked more easily to ethylene. This feature still further reduces the formation of by-products, especially the formation of solid carbonaceous deposits in the vapor phase cracking zone.

I have also discovered that in the low temperature combined hydrogenation and crackingr step pyrolusite serves as a highly emcient catalyst for the desired reaction. The pyrolusite may be employed in its native form without any further treatment other than crushing to the desired granule size.

In conducting the vapor phase cracking step of my process I employ a novel combination of conditions which I have found to yield a greater conversion of the hydrocarbon to ethylene than conditions previously employed. In this step of my process I form a mixture of steam and hydrocarbonl vapor ori gas in any suitable manner containing a weight ratio of steam to hydrocarbon between 1:1 and 3: 1. This mixture should be substantially free of elemental hydrogen. I then pass the mixture through a reaction zone maintained at a temperature between '780 and 1050 C. at such a rate that the mixture is at a temperature of 780 C. or above for a time such that logro of time in seconds is not more than 11080 T 9.8 and not less than where T is the temperature expressed in degrees Kelvin. These conditions I have found to be most satisfactory whether the hydrocarbon is a substantially pure compound such as ethane,

. propane, butane, etc., or a mixture of compounds,

such asgas oil, kerosene, crude petroleum, topped petroleum, or the product of my low temperature combined hydrogenation and cracking step.

While the above vapor phase cracking process is applicable to crude petroleum, the heavier constituents of the petroleum (those boiling above about`300 C.) tend to deposit carbon in the reaction zone and give reduced yields of ethylene. This disadvantage may be practically completely avoided by subjecting such constituents to a treatment with hydrogen at a temperature between about 400 and about 500 C. and a pressure between about 50 and about 200 atmospheres for a period of around 1 to 30 hours. While still higher pressures may be used, the practical difficulties of compression offset to a considerable extent the additional advantages gained. The hydrogen gas employed for this step preferably should be a highly concentrated hydrogen, or if it is diluted with other constituents, the pressure should be increased correspondingly. The yields of ethylene-forming reaction -products are increased by use of a pyrolusite catalyst which reduces the proportions of carbon and asphaltic materials produced. While it has in the past been proposed to subject hydrocarbon vapors to the combined action of high temperature and hydrogen in the production of ethylene, it has been my experience that the effect of the hydrogen upon the ethylene is far more energetic than its effect upon the higher hydrocarbons which I desire to hydrogenate and that accordingly such processes tend to diminish the yield of ethylene and increase the yield of ethane. On the other hand, once the hydrogen is introduced into the higher hydrocarbons, it does not seem to have this effect upon the ethylene during the subsequent vapor phase cracking step. Some free hydrogen is formed by the cracking in vapor phase but the amount thus formed is relatively small. A small amountl of air or oxygen may be mixed with the vapors passing to the cracker to burn up this hydrogen. This' air or oxygen also will supply heat and assist in maintaining the desired cracking temperatures.

The attached drawing shows a flow diagram of a complete process for converting crude petroleum to ethylene. y

The followingexample will further illustrate the manner in which my invention may be applied to the production of ethylene from crude petroleum:

Example-A mixture of crude petroleum and crushed butotherwise untreated pyrolusite is introduced into a direct-fired vessel capable of withstanding high pressure and hydrogen is introduced until the hydrogen pressure is approximately 200 atmospheres. While this pressure is maintained, the mixture is heated to 450 C. and maintained at this temperature for an average time of around two hours. During the reaction period hydrogen is continuously bubbled through the liquid and hydrogen together with vapors formed is gradually withdrawn. Additional petroleum is added to maintain the liquid volume as the cracking proceeds. The`vapors are condensed from residual hydrogen and the condensate is then reheated in liquid phase to around 200 C. (under suiilcient pressure to maintain the liquid phase). At this temperature the liquid is injected intoa stream of steam previously superheated to around 1000 C. in a ratio oi' 1.7 parts by weight of steam to each one part by weight of oil and the resulta nt steam-hydrocarbon vapor mixture is immediately passed at a pressure between about l and about 11/2 atmospheres absolute into contact with a bed of refractory material (for instance, clay-bonded silicon carbide crushed to a particle size passing a 2 inch mesh screen and retained on a 1 inch mesh screen) previously heated to 1050 C., the rate of flow being controlled so that the time during which the mixture is above 850 C. is about 0.03 second. The stream of reaction products is then cooled to a temperature between 300 and 400 C. The partially cooled gases and vapors are then passed countercurrent to a flow of tar to further cool them to around 100 to 150 C. and wash out the tarry liquid condensate formed. The gases are then brought into contact with water to cool them tonormal temperature and condense remaining liquid constituents.

Since the total condensate of the above two cooling steps would have a density approximately that .of water and would tend to emulsify therewith if collected as a single condensate. it is preferred to condense the higher and lower boiling `condensates separately. The second condensate has a substantially lower density than water and may be separated readily therefrom.

The passage of steam-hydrocarbon mixture into contact with the refractory may be continued until the temperature of the refractory has dropped to about 850 C. In this connection it is noted that while the temperature of steam is initially as high as or higher than that.

of the refractory material, the cracking reaction is endothermic and requires more heat than provided by the limited amount of steam present during the cracking operation. Furthermore,- the temperature of the steam may be as low as 100 C. or as high as 1500 C. but higher temperature steam, say between 800-1500 C., is to be preferred because it permits the more rapid heating of the oil vapor and use of a smaller reaction zone. This is desirable from the standpoint of both heat economy and ethylene yield.

Any suitable apparatus may be used for conducting the vapor phase cracking step of this invention. However the apparatus described and illustrated in' U. S. patent application Serial No. 153,496, led July 14, 1937, by Frank Porter and John Moyle Duncan, is highly satisfactory and may be used toadvantage.

By the above process I am able to obtain a gas containing between 30 and 40 mol percent of ethylene. The gas will also contain on the order of 25 mol percent methane, 15 mol per cent hydrogen, around 5 to 25 mol percent of propylene and butylene, around 5 mol percent of ethane. and relatively small proportions of propane, butanes, pentanes, pentenes, benzene, carbon monoxide, and carbon dioxide. The ethylene may be separated from such of these products as desired in known manner.

My process of combined hydrogenation and cracking followed by vapor phase cracking is to be distinguishedk from prior procedures involvl ing merely a liquid phase cracking followed by a vapor phase cracking. For example, in the treatment of a topped crude petroleum my process involving liquid phase hydrogenation and cracking followed by vapor phasel cracking yielded, in a single pass, an amount of ethylene corresponding to about) 25.2% of the topped crude. By recycling the condensate from the vapor phase cracking step a yield of ethylene equal to 37.2% of the topped crude may be obtained.

I claim:

1. The method of forming ethylene from petroleum hydrocarbons having a. boiling point above about 300 C., which `comprises subjecting such hydrocarbons in liquid phase to a combined hydrogenation and cracking at a temperature between 400 and 5905,01, and subjecting the resultant hydrogenatiorryracking product to vapor phase cracking 'at a temperature between 780 and 1050 C. to convert hydrogenation cracking products to ethylene.

2. The method oi'l forming ethylene from petroleum hydrocarbons` having a boiling point above about 300 C., which, comprises swbjecting such hydrocarbons -to contact with hydrogen at a temperature between 400 and 500 C. in liquid phase to crack and hydrogenate such hydrocarbons, and subjecting the resultant product to vapor phase cracking in admixture with from 1 to 3 parts by weight of steam for each 1 part by weight of hydrocarbon at a temperature between 780" and 1050 C. for a time such that login oi' time in seconds is not more than and not less than Where T is the temperature expressed in degrees Kelvin.

3. In the manufacture of ethylene from petroleum hydrocarbons having a boiling point above about 300" C. by a process involving a combined hydrogenation and cracking of the hydrocarbons in liquid phase and subsequent vapor phase cracking of products thereof, the imleum hydrocarbons having a boiling point above about 300 C. by a process involving a combined hydrogenation and cracking of the hydrocarbons vin liquid phase and subsequent vapor phase cracking of products thereof, the improvement which comprises conducting said combined hy-v drogenation and cracking of the hydrocarbons in liquid phase at a temperature between'400 C. and 500 C. in contact with a catalyst comprising pyrolusite.

5. In the manufacture of ethylene from petroleum hydrocarbons having a boiling point above about 300 C. by a process involving a combined hydrogenation and cracking of the hydrocarbons in liquid yphase and subsequent vapor phase cracking of products thereof, the improvement which comprises conducting said combined hydrogenation and cracking of the hydrocarbons in liquid phase at a temperature between 400 and 500 C. and a pressure between about 50 and about 200 atmospheres in contact with a catalyst comprising pyroiusite.

6. The method of forming ethylene from petroleum hydrocarbons having a boiling point above about 300 C., which comprises subjecting a mixture of such hydrocarbons and pyroiusite to contact with hydrogen at a temperature between 400 and 500 C. and at a. pressure of at least 50 atmospheres in liquid phase to crack and hydrogenate such hydrocarbons, and subjecting the resultant product to vapor phase cracking in admixture with from 1 to 3 parts by Weight of steam for each 1 partby weight of Ahydrocarbon at a temperature between 780 and 1050 C. for

a time such that login of time in seconds is not more than where T is the temperature eirpressed in degrees Kelvin. f

7. The method of forming ethylene from petroleum hydrocarbons having a boiling point above about 300 C., which comprises subjecting a mixture of such hydrocarbons and pyrolusite to contact with hydrogen at a `temperature between 400 and 500 C. and a pressure between about and about 200 atmospheres, separating condensible hydrocarbon products from hydrogen,

introducing said' hydrocarbon products in liquid Where T is the temperature expressed in degrees Kelvin. l

FRANK PORTER. 

